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Apart from a second, intervals can be described as either {Diminished, Perfect, Augmented} or {Dim, Minor, Major, Aug} depending on whether or not the major and minor scale share that interval. For example, both the major and minor scale contain a perfect fifth yet they do not share a major/minor 3rd or 6th. This is true for all intervals except for the second. Both the major and minor scale have a major second, so why is it not called a perfect second? I think this would make more sense when learning why certain intervals are be perfect and not major/minor and it also makes more sense when listening to intervals as a minor second interval has the same sort of dissonance that a diminished 5th does so calling it a diminished second could make more sense.

In summary, why are seconds called minor/major?

marked as duplicate by Neil Meyer, Shevliaskovic, Doktor Mayhem Jan 22 '16 at 13:32

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The minor intervals are not minor because they are found in the minor scale and the same goes for major intervals. The intervals are concepts based on the distance between two notes based on letter name and absolute distance in semitones.

It should also be noted that the term major and minor is used a lot in music and when applied to interval major means further in distance and minor means smaller. In some ways, you can view a minor interval as a half step or semitone above the previous interval set and a major interval as a whole step or tone above the previous interval.

To better explain why the intervals ended up this way, let's look at this solely from a distance perspective at first. The distances from unison to octave are as follows in semitones:

 0 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12

In C these notes would map to:

 C - Db - D - Eb - E - F - F#/Gb - G - Ab - A - Bb - B  - C 

As you can see, both 0 and 12 map to C and the furthest you could be away from a C in semitones is 6. This leaves us with 5 notes on each side with 1 - 2 - 3 - 4 - 5 closer to 0 and 7 - 8 - 9 - 10 - 11 closer to 12.

Now let's look at the standard interval names. In this I will use M for major, m for minor, P for Perfect and tt for tritone (which is considered both an augmented 4th and a diminished 5th).

 P1 - m2 - M2 - m3 - M3 - P4 - tt - P5 - m6 - M6 - m7 - M7 - P8

Now looking at the whole interval spectrum, we notice

  • The tritone (or 6 semitones away) has a perfect interval above and below (P4 - tt - P5) and can be described as both an A4 and d5 for this reason.
  • The note you are basing the name off of (C in this case which is both 0 and 12) is also perfect (P1 for unison P8 for octave) .
  • The other notes are group into twos (because of the two semitones typical max in scales) with the smaller one being minor and the bigger one being major (m2 - M2 - m3 - M3) and (m6 - M6 - m7 - M7).
  • The augmented and diminished intervals of the major and minor intervals are for when one of the intervals stretches out of its typical designation.

So in short, a major interval just means it's the bigger of a set of two possible intervals. The fact that the minor scale uses it is kind of irrelevant in this naming scheme.

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Perfect intervals are called that because there is a purity to there sound that is not present in the other intervals. Second intervals have a distinct dissonant quality to them that is really very different to the perfect intervals.

This idea is most evident when you hear a modulation pedal in effect. Listen to the seconds it has a distinct uneasy quality to it where the fifths and the octaves sound much less dissonant.

Take a look at this video it illustrate it well.

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    Thus it could be argued that a major third, with its consonant sound, could be called perfect? Major sixth is similar. – Tim Jan 22 '16 at 7:54
  • I would say that thirds even though more consonant than seconds still do not entirely have the purity of a perfect interval. – Neil Meyer Jan 22 '16 at 8:11
  • Purity is in the mind (well, ear) of the beholder. – Carl Witthoft Jan 22 '16 at 12:34
  • Perfect 4ths are actually considered dissonant in classic theory. It's why second inversion chords needed to be approached with care. – Dom Jan 22 '16 at 13:37
  • @Dom - I'd have said that a second inversion chord sounds more stable than a first inversion. Most stable is root. Stable and dissonant not being exactly the same, but having the same connotation? – Tim Jan 24 '16 at 8:31
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Music theory is an evaluation. The ratio's (the nomenclature of the intervals) were developed by Pythagoras with his string. Perfect are only three unison/octave, fifth, and fourth. That is due to ratios. The more the ratios are dessonsonant they stop from getting the nomenclature of a perfect.

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